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F W Smith

Publications and source records attributed to F W Smith.

At least 55 records · Page 3Linked to original sources
PubMed1996

A variable threshold edge-detector for improved quantitation of gated tomographic imaging of the left ventricular blood pool.

The accurate measurement of left ventricular volume from tomographic MUGA studies is difficult due to the limited resolving power of the gamma camera, which causes errors in the detection of the correct ventricular boundaries. Therefore, the use of fixed threshold or second-derivative edge-detectors results in overestimates at small volumes. A variable threshold edge-detection technique was developed to overcome this. Computer-simulated short-axis slices through the heart over a range of left ventricular dimensions were convolved by the Point Spread Response Function of the system to model the acquired image. The maximum pixel value and the threshold value required to detect the true ventricular edge from each simulation were then combined into a look-up table for the calculation of the required threshold value. As the dimension of the ventricle decreased, the threshold value chosen to detect the ventricular edge increased. Left ventricular volumes and ejection fraction measurements were calculated for seven patients using cine-MRI as the gold-standard technique for validation of the proposed method. The single photon emission tomographic studies were analysed using both the standard second-derivative edge-detection software and the proposed variable threshold technique. The variable threshold technique was shown to increase significantly the accuracy of ventricular volume measurements and ejection fraction calculations. The average error in the measurement of volumes was reduced from 41.4 +/- 45.1% to 18.5 +/- 14.6% and the accuracy of ejection fraction measurement was increased from 29.7 +/- 4.6% to 11.3 +/- 6.9%.

Algorithms↗
PubMed1996

Clinically suspected scaphoid fracture: a comparison of magnetic resonance imaging and bone scintigraphy.

59 patients with clinical suspicion of scaphoid fracture, but negative radiographs at presentation and review, were examined by magnetic resonance imaging (MRI) and bone scintigraphy (BS). The diagnoses were compared with subsequent follow-up. There were four scaphoid fractures, 10 other fractures and three significant ligamentous injuries. All scaphoid fractures were identified by MRI and BS. MRI showed better interobserver agreement for scaphoid injury than BS and fewer false positive reports. Significant ligamentous injury and carpal instability diagnosed by MRI were not evident on scintigraphy. Using fast scanning protocols, the cost of MRI is comparable with that of BS. MRI should be considered as the appropriate second line investigation in these clinical circumstances.

Adolescent↗
PubMed1996

Decompression illness in sports divers detected with technetium-99m-HMPAO SPECT and texture analysis.

UNLABELLED: Diving for sport and recreation has increased in recent years, resulting in more incidences of diving illness. Therefore, we studied potential use of regional cerebral blood flow SPECT imaging with 99mTc-HMPAO in the management of divers who have experienced decompression illness (DCI). METHODS: A group of ten sports divers who had no experience of DCI were compared with ten sports divers who had experienced at least one episode of DCI. Transaxial SPECT images were first compared objectively using a first-order texture measure and then subjectively using a receiver operator characteristic (ROC) experiment. Experienced observers were asked to rate images subjectively in terms of the images' textural appearance. RESULTS: Both these techniques showed that there is a statistically significant difference between the two groups and the images produced by the DCI divers were generally more coarsely patchy when compared to the non DCI divers. The quantitative texture technique proved significantly better in identifying divers with DCI than the visual analysis by observers using ROC curves. CONCLUSION: Differences between the cerebral blood flow patterns of sports divers who have experienced DCI and sports divers who have no experience of DCI can be detected using 99mTc-HMPAO SPECT and a texture analysis technique.

Adult↗
PubMed1996

Pre-surgical dental implant assessment by magnetic resonance imaging.

The use of magnetic resonance imaging (MRI) for pre-surgical implant assessment of available bone in the maxilla and mandible is described. An acrylic surgical template with suitable MRI reference markers allows potential implant sites, as chosen on the MR images, to be accurately identified at surgery. MRI is a tomographic modality capable of giving accurate information on the three-dimensional relationships of all the relevant anatomic structures. Our results show that MRI is reasonably tolerant of artifacts caused by metal pins and amalgam fillings. Unlike computerized tomography (CT) and other x-radiographic techniques, MRI uses no ionizing radiation, and is capable of angulating and offsetting its scan plane at will. Good bone detail is available because cancellous bone yields a strong signal from the marrow fat, while cortical bone and dental enamel are dark. The excellent anatomic detail provided by thin-slice high-resolution MRI allows for assessment of the suitability of sites to receive an implant in terms of bone quality and thickness, and the relative position of the site to important structures such as the inferior dental nerve and nasal sinuses. The MRI technique used is described in detail. The principles underlying image contrast are outlined where appropriate and examples shown. To date, we have used MRI in conjunction with rotational panoramic x-rays (OPG) to plan 26 implants (21 maxillary, 5 mandibular) in 12 patients.

Alveolar Bone Loss↗
PubMed1995

Promoter elements of the PHR1 gene of Saccharomyces cerevisiae and their roles in the response to DNA damage.

The PHR1 gene of Saccharomyces cerevisiae encodes the apoenzyme for the DNA repair enzyme photolyase. PHR1 transcription is induced in response to 254 nm radiation and a variety of chemical damaging agents. We report here the identification of promoter elements required for PHR1 expression. Transcription is regulated primarily through three sequence elements clustered within a 120 bp region immediately upstream of the translational start site. A 20 bp interrupted palindrome comprises UASPHR1 and is responsible for 80-90% of basal and induced expression. UASPHR1 alone can activate transcription of a CYC1 minimal promoter but does not confer damage responsiveness. In the intact PHR1 promoter UAS function is dependent upon an upstream essential sequence (UES). URSPHR1 contains a binding site for the damage-responsive repressor Prp; consistent with this role, deletion or specific mutations of the URS increase basal level expression and decrease the induction ratio. Deletion of URSPHR1 also eliminates the requirement for UESPHR1 for promoter activation, indicating that the UES attenuates Prp-mediated repression. Sequences within UASPHR1 are similar to regulatory sequences found upstream of both damage responsive and nonresponsive genes involved in DNA repair and metabolism.

Apoenzymes↗
PubMed1995

Solution structures of unimolecular quadruplexes formed by oligonucleotides containing Oxytricha telomere repeats.

BACKGROUND: Oligonucleotides containing the guanine-rich telomeric sequence of Oxytricha chromosomes (dT4G4) have previously been shown to form DNA quadruplexes comprising guanine quartets stabilized by cations. Two different structures have been reported for both d(G4T4G4) (Oxy1.5) and d(G4T4G4T4G4T4G4) (Oxy3.5). RESULTS: Here we present the solution structure of a uracil- and inosine-containing derivative of Oxy3.5, d(G4TUTUG4T4G4UUTTG3I) (Oxy3.5-U4128), determined using two-dimensional 1H and 31P NMR techniques. This oligonucleotide forms a unimolecular quadruplex that is very similar to the dimeric Oxy1.5 solution structure, in that it contains a loop spanning the diagonal of an end quartet. The groove widths, strand polarities, and positions of the syn bases along the G4 tracts and within the quartets are all as reported for Oxy1.5. The first and third pyrimidine tracts form parallel loops spanning a wide groove and a narrow groove respectively. CONCLUSIONS: Both Oxy3.5 and Oxy3.5-U(4)128 form unimolecular quadruplexes in solution with a diagonal central T4 loop. These results conflict with those reported for d(G4TUTUG4TTUUG4UUTTG4) in solution, in which the central loop spans a wide groove.

Animals↗
PubMed1995

Plant members of a family of sulfate transporters reveal functional subtypes.

Three plant sulfate transporter cDNAs have been isolated by complementation of a yeast mutant with a cDNA library derived from the tropical forage legume Stylosanthes hamata. Two of these cDNAs, shst1 and shst2, encode high-affinity H+/sulfate cotransporters that mediate the uptake of sulfate by plant roots from low concentrations of sulfate in the soil solution. The third, shst3, represents a different subtype encoding a lower affinity H+/sulfate cotransporter, which may be involved in the internal transport of sulfate between cellular or subcellular compartments within the plant. The steady-state level of mRNA corresponding to both subtypes is subject to regulation by signals that ultimately respond to the external sulfate supply. These cDNAs represent the identification of plant members of a family of related sulfate transporter proteins whose sequences exhibit significant amino acid conservation in filamentous fungi, yeast, plants, and mammals.

Amino Acid Sequence↗
PubMed1995

Isolation of a cDNA from Saccharomyces cerevisiae that encodes a high affinity sulphate transporter at the plasma membrane.

Resistance to selenate and chromate, toxic analogues of sulphate, was used to isolate a mutant of Saccharomyces cerevisiae deficient in the capacity to transport sulphate into the cells. A clone which complements this mutation was isolated from a cDNA library prepared from S. cerevisiae poly(A)+ RNA. This clone contains an insert which is 2775 bp in length and has a single open reading frame that encodes a 859 amino acid polypeptide with a molecular mass of 96 kDa. Sequence motifs within the deduced amino acid sequence of this cDNA (SUL1) show homology with conserved areas of sulphate transport proteins from other organisms. Sequence analysis predicts the position of 12 putative membrane spanning domains in SUL1. When the cDNA for SUL1 was expressed in S. cerevisiae, a high affinity sulphate uptake activity (Km = 7.5 +/- 0.6 microM for SO2-4) was observed. A genomic mutant of S. cerevisiae in which 1096 bp were deleted from the SUL1 coding region was constructed. This mutant was unable to grow on media containing less than 5 mM sulphate unless complemented with a plasmid containing the SUL1 cDNA. We conclude that the SUL1 cDNA encodes a S. cerevisiae high affinity sulphate transporter that is responsible for the transfer of sulphate across the plasma membrane from the external medium.

Amino Acid Sequence↗
PubMed1995

Positron emission tomography: 2-deoxy-2-[18F]-fluoro-D-glucose uptake in locally advanced breast cancers.

Fifteen patients with locally advanced breast cancers were studied using the radiopharmaceutical 2-deoxy-2-[18F]-fluoro-D-glucose (FDG) with positron emission tomography (PET). Five patients were sequentially imaged before and after two pulses of chemotherapy. In 14 of 15 tumours increased uptake of FDG was observed which correlated with the clinical site of the tumour. The PET images were compared with the mammographic and ultrasonomammographic appearances of the tumours in selected patients. In two patients with normal mammograms PET imaging detected the tumour and in a further four patients, with suspicious but not conclusively malignant mammographic changes, a well-defined area of increased FDG uptake was demonstrated by PET. In all five sequentially imaged tumours, following chemotherapy, there was a decrease of the FDG tumour: normal breast uptake ratio. In four patients who completed a full chemotherapeutic course this change preceded a pathological response of their tumours. These findings suggest that this technique may be of benefit in imaging carcinomas in the breasts of pre-menopausal women which may appear dense on mammography and moreover, that sequential imaging may have a role in the prediction, at an early stage, of the response of locally advanced carcinomas to chemotherapy.

Adult↗
PubMed1995

Texture analysis of divers' brains using 99Tcm-HMPAO SPET.

The potential use of regional cerebral blood flow (rCBF) single photon emission tomography (SPET) imaging with 99Tcm-hexamethylpropyleneamine oxime (HMPAO) in the management of divers who have undergone a form of decompression sickness (DCS) was investigated using texture analysis. We imaged 50 divers, 10 of whom had only experienced DCS which had been categorized as Type 1, 20 of whom had a history of DCS classified as Type 2 and 20 of whom had not suffered an episode of DCS. A number of divers who had experienced Type 2 DCS had also had incidents of Type 1. The reconstructed SPET images were pre-processed and analysed using a first-order texture analysis technique based on a grey level histogram. The results showed that there was a significant textural difference between the divers who had only suffered episodes of DCS Type 1 and the diving controls and a difference between the divers with a history of Type 2 and the diving controls. No differences were found between the two groups of divers who had a history of DCS. This result suggests that DCS produces a detectable change in 99Tcm-HMPAO SPET brain images. However, the segmentation between the groups investigated was not complete and so the usefulness of this approach appears limited in individual cases but may provide useful information about the effects of different diving practices.

Adult↗
PubMed1995

Superimposition of PET images using 18F-fluorodeoxyglucose with magnetic resonance images in patients with pancreatic carcinoma.

Six patients with histologically proven adenocarcinoma of the pancreas were studied using 2-deoxy-2-[18F]-fluoro-D-glucose (18F-FDG) using positron emission tomography (PET), and magnetic resonance imaging (MRI). In all six cases there was avid accumulation of 18F-FDG within the pancreatic tumour and clear visualization of the tumour on the MRI images. Delineation of the tumours was aided by superimposition of the images from the two imaging methods, which was achieved by using a system of surface markers.

Adenocarcinoma↗
PubMed1995

Aortic distensibility and stiffness index measured by magnetic resonance imaging in patients with Marfan's syndrome.

OBJECTIVES: To use magnetic resonance imaging to measure the elastic properties of the aorta of adults with Marfan's syndrome and to compare these results with those obtained by echocardiography. PATIENTS AND METHODS: 12 patients with Marfan's syndrome and 12 controls matched for age. Transverse luminal areas of the ascending and descending aorta were measured using electrocardiographic gated magnetic resonance imaging. Echocardiography was used to measure the diameter of the ascending aorta and aortic arch in patients with Marfan's syndrome. Blood pressure was measured during both scans. RESULTS: In diastole, transverse luminal areas of the ascending and descending aorta were significantly greater in patients with Marfan's syndrome when measured by magnetic resonance imaging and corrected for body surface area; P < 0.02 and P < 0.05 respectively. Patients with Marfan's syndrome had a higher stiffness index (112.77 v 5.78, P < 0.05) and a lower distensibility (0.0066 v 0.0105, P < 0.05) than controls. Results produced by MRI and echocardiography were not significantly different. CONCLUSIONS: Magnetic resonance imaging gives good quality reproducible images of the ascending and descending aorta. In patients with Marfan's syndrome, aortic distensibility and stiffness index measured by magnetic resonance imaging were abnormal (but did not always relate directly to the size of the aorta.

Adult↗
PubMed1994

d(G3T4G3) forms an asymmetric diagonally looped dimeric quadruplex with guanosine 5'-syn-syn-anti and 5'-syn-anti-anti N-glycosidic conformations.

The structure formed by the DNA oligonucleotide d(G3T4G3) has been studied by one- and two-dimensional 1H NMR spectroscopy. In NaCl solution, d(G3T4G3), like d(G4T4G4) (Oxy-1.5), forms a dimeric quadruplex with the thymines in loops across the diagonal of the end quartets. Unlike Oxy-1.5, the dimer is not symmetric, and both monomer strands are observed in NMR spectra. Three quartets are formed from the GGG tracts. Glycosidic conformations of the guanines are 5'-syn-syn-anti-(loop)-syn-anti-anti in one strand and 5'-syn-anti-anti-(loop)-syn-syn-anti in the other strand. Thus, the stacking of the quartets (tail-to-tail, head-to-tail) is unlike all previously described fold-back (tail-to-tail, head-to-head) and parallel-stranded (head-to-tail, head-to-tail) quadruplexes.

Base Sequence↗
PubMed1994

Refined solution structure of the dimeric quadruplex formed from the Oxytricha telomeric oligonucleotide d(GGGGTTTTGGGG).

BACKGROUND: Telomeres, the structures at the ends of linear eukaryotic chromosomes, are essential for chromosome replication and stability. The telomeres of the unicellular ciliate Oxytricha contain a 3' single strand overhang composed of two repeats of the telomere repeat sequence d(TTTTGGGG). It has been proposed that oligonucleotides containing this repeat can form DNA quadruplexes via hydrogen bonding of the guanines into quartets. Such structures may be relevant to the biological function of the telomere, and in G-rich sequences elsewhere in the genome. RESULTS: We have previously determined from solution NMR data that the Oxy-1.5 Oxytricha repeat oligonucleotide d(GGGGTTTTGGGG) dimerizes to form an intermolecular quadruplex composed of four guanine quartets and with the thymines in loops across the diagonal at opposite ends of the quadruplex. We report here the refined solution structure of Oxy-1.5. This structure is compared with the previously published crystal structure of the same oligonucleotide. CONCLUSIONS: Oxy-1.5 forms a well-defined, symmetrical structure with ordered thymine loops. Both the solution and crystal structures of Oxy-1.5 are quadruplexes with alternating syn and anti glycosyl conformation of guanines along each strand of the helix and have thymine loops at opposite ends. However, the topology of the two structures is fundamentally different, leading to significant structural differences. A topological pathway for the formation and interconversion of the two structures is proposed.

Animals↗
PubMed1994

Evaluation of tilted, optimized, non-saturating excitation pulses in 3D magnetic resonance angiography of the abdominal aorta and major branches in volunteers.

Ten normotensive volunteers were imaged with FISP-3D (Fast Imaging Steady Precession) pulse sequences (a steady state gradient recalled echo, SS-GRE, technique) without and with modification by tilted, optimized non-saturating excitation (TONE) customized radio frequency (RF) pulses, for evaluation of the abdominal aorta--in particular the renal arteries. Maximum intensity projection (MIP) angiograms were constructed for each sequence in each volunteer; 15 observers "blinded" to sequence type preferred the images generated from the TONE applied sequence. Analysis showed that this preference was significant.

Aorta, Abdominal↗
PubMed1994

Technical note: use of a double inversion recovery pulse sequence to image selectively grey or white brain matter.

The design of a double inversion recovery (DIR) sequence, to image selectively grey or white brain matter, is described. Suitable choice of inversion times allows either cerebrospinal fluid (CSF) and white matter to be suppressed, to image the cortex alone, or CSF and grey matter to be suppressed, to image the white matter. The DIR sequence was found to give clear delineation of the cerebral cortex.

Adult↗